Composite structures made from fibrous materials, such as Fiberglas.RTM., graphite fibers and various resins, such as epoxy, are finding increased use as substitutes for metal in aircraft and other structures. It is well known that composite structural elements can be specifically designed for various structural purposes by selecting the appropriate filament direction and laminate structure of the composite.
The use of composites in structural members such as I-beams and flanges has presented a particular problem. It is known that the junction between two perpendicular composite layers is prone to peeling. U.S. Pat. No. 3,995,080, issued to Cogburn et al., describes the use of fillers (fillets) which are radiused to conform to the junction between perpendicular composite structures, such as the web and flange sections of an I-beam.
In U.S. Pat. No. 4,331,723 issued to Hamm and assigned to the assignee of the present invention, the use of composite fillers is described in conjunction with additional reinforcing structure.
Fillers of the type described above are generally triangular in cross section. Two adjacent sides of the filler are radiused to conform to curvature at the junction of the perpendicular composite structures.
Formation of the fillers is a tedious, laborintensive, and expensive procedure. The conventional method for forming fillers includes a series of manual steps. In the first step, a section of composite material which has been pre-impregnated with resin is folded or rolled to form a roughly rectangular or cylindrical shape. Where the filler is designed for use in an elongated structural member such as an I-beam, the filler must be provided with a length equal to the structural member; the filler may be a few inches long, five feet long, six feet long, or longer. The pre-impregnated composite tape is difficult to handle because it is generally tacky at room temperature. It is very difficult to fold this material into a rectangular or triangular cross section having a width of approximately 1/4" because of the tackiness. Furthermore, substantial nonuniformity in the folded material is unavoidable.
After the composite material has been rolled or folded into an elongated shape, the material is roll-formed in a second step by a conventional roll-forming machine to produce the desired triangular cross section with radii on two adjacent sides. Nonuniformities in the folded material can jam the roll-forming machine.
Therefore, a need exists for a simplified, economical method of forming radius fillers for composite structures.